Method for continuous production of foamed plastic objects



April 26, 1966 c. R. WlLES ETAL METHOD FOR CONTINUOUS PRODUCTION OFFOAMED PLASTIC OBJECTS Original Filed Sept. 1, 1961 INVENTORS. Char/esR. Wi/es Kenna/h R. Hi/fon BY ZNT United States Patent METHOD FORCQNHNUOUS PRODUCTESN 0F FGAhiEl) PLASTIC Gil-.llECTS Charles R. Wiles,Midland, and Kenneth R. Hilton, Har rlson, Mich, assignors to The DowChemical Company, Midland, Micln, a corporation of Delaware Griginalapplication Sept. l, 1961, Ser. No. 135,494, new Patent No. 3,196,484,dated July 27, 1965. Divided and this application duly 2%, 1963, Ser.No. 298,6)92

7 Qlairns. (Cl. 264- 85) This application is a divisional application ofour copending application Serial No. 135,494, filed September 1, 1961,now United States Letters Patent 3,196,484,

This invention relates to an improved method and apparatus for theforming of expanded thermoplastic resinous articles. It moreparticularly relates to a method and apparatus for the continuousforming of particulate expandable thermoplastic material into foamedplastic objects.

Foam plastic bodies are prepared in a variety of manners among which isa method comprising heating an un foamed or partially foamed particulatemass of organic thermoplastic resinous material confined within a moldto expand the material and cause it to knit together into a coherentunitary object. Various methods are employed to form such bodies as themethods described in United States Patents 2,787,809 and 2,744,291,wherein a particulate mass confined in a mold is immersed in a hotliquid.

Employing these techniques, it is necessary to form each foamed plasticbody by what amounts to a repetitive step. Such a step involvesemploying two mating mold halves, placing an expandable material withinthe mold cavity, heating the particulate material to expand, fill themold cavity, and knit together to form a unitary object, subsequentlythe molded foam objects are cooled, the mold opened, and the partremoved. Thus, for each object formed, two mold halves are employed andthe entire mold assembly must be heated and cooled.

It is an object of this invention to provide a continuous method offorming expandable particulate thermoplastic material into a pluralityof identical objects.

It is a further object of this invention to provide a method andapparatus for the continuous molding of foamed thermoplastic objectsfrom particulate expandable thermoplastic resinous material.

It is still another object of this invention to provide an apparatus forthe continuous molding of foamed thermoplastic objects employing moldswhich form one face of an object and serve to shape the opposite face ofa like object.

In accordance with the method of the invention, these objects and otheradvantages may be attained by providing a first mold having a desiredconfiguration, placing within said desired configuration a quantity ofresinous thermoplastic expandable material, placing adjacent said firstmold a second mold having a desired configuration, confining saidexpandable thermoplastic material by means of said first and secondmolds, adding expandable thermoplastic material to the configuration ofsaid second mold and confining the material therein with a third moldcontinually sequentially heating said molds and contents thereof to atemperature sufficient to expand the particulate thermoplastic material,sequentially cooling said molds and removing the formed foamedthermoplastic objects therefrom. I

Also within the scope of the invention is an apparatus for continuouslyforming foamed thermoplastic objects, said apparatus comprising incooperative combination a plurality of molds, a housing defining apassageway adapted to receive said molds, said passageway having atleast two portions, a heating portion and a cooling portion,

ice

said molds being so constructed and arranged that on being placedadjacent to each other in a configuration which may be forced throughsaid passageway a cavity is defined between each of said molds havingshape of the object desired to he formed.

Further features and additional advantages and benefits of the presentinvention will be more fully manifest in the ensuing description andspecification, taken in connection with the accompanying drawingwherein:

FIGURE 1 is a schematic sectional View of an apparatus in accordancewith the invention and illustrating the method thereof.

FIGURE 2 is an enlarged representation of a plurality of molds withinthe apparatus of FIGURE 1.

FIGURE 3 shows an object formed from expandable thermoplastic resinousmaterial in accordance with the invention.

In FIGURE 1 there is illustrated a schematic cross sectional view of anapparatus in accordance with the invention generally designated by thereference numeral 10. The apparatus 10 comprises a conduit 12 defining apassageway 13. The conduit 12 is comprised of a heating section 314 anda cooling section 15. The heating section 14 is wrapped with anelectrical conductor 16 connected to a source of alternating current 18.A plurality of molds 26 are provided which slidably engage the innersurfaces of the passageway 12. A hopper 22 is provided adjacent theuppermost portion of the heating section 14 which also is adapted toslidably engage the molds 20. The mold Zlla contains on its innersurface a particulate foamable thermoplastic resin 23. A portion of theresin 23 is also disposed within the hopper 22. The resinous material 23is contained between the molds b and 200 and expanded, substantiallyfilling the void between the molds. The conduit portion 15 is providedwith a cooling jacket 25 which is equipped with an inlet 26 and anoutlet 27. The space between the conduit portion 15 and the jacket 25 isdivided into two portions by diametrically opposed dividers 28 (oneshown). A plurality of openings 29 provide communication betweenpassageway 13 and the interior of jacket 25. The cooling portion 15 ofthe conduit 12 terminates in a mold exit 34).

In FIGURE 2 there is illustrated a schematic cross sectional view of amating pair of molds, so nested in accordance with the invention as theywould appear toward the terminal portion of the heating section 14 ofthe apparatus of FIGURE 1. The molds 20 are comprised of a magneticferrous metal such as iron or steel body section 35 defining a cavity37, the inner wall of body portion 35 is provided with a non-magneticconductive liner 3%, prepared from metals such as aluminum, copper, andthe like, and adjacent the rim of the body portion 35 is a non-magneticconductive metal sleeve 39. Disposed between adjacent molds 26 is a thinplastic film liner 42. Surrounding the liner 42 and within the cavity 37of the mold 2% is a unitary foamed plastic body 43.

FIGURE 3 shows a cutaway view of cup formed in accordance with theinvention. The cup Sll comprises a foamed portion 43 rigidly adhere to aliner 42.

In operation of the illustrated embodiment of the invention, the wallsof the mold 20 defining the cavity 37 are treated with an adhesive toprovide uniform distribution of particulate expandable material. Aparticulate thermoplastic mass 23 is introduced into the mold in such amanner that the walls thereof are uniformly covered with the expandableparticulate plastic. A preformed thin thermoplastic cup liner such asthe liner 42 is positioned on the mold 20 opposite the side carrying theexpandable thermoplastic material 23. A series of such molds areintroduced into the apparatus 10 through the hopper 22 whereinadditional granular thermoplastic material 23 is provided to fill thespace between adjacent molds. Alternating current is provided to thewinding 16 which induces a current in the molds 20. The heating of themolds 2% causes the expandable thermoplastic material between adjacentmolds to expand and knit together into a unitary body and bond to theliner 42. The molds 20 are advanced through the heating portion 14 intocooling portion 15 where the heat added to the mold by the inductionheater is removed and the thermoplastic material between adjacent moldssoliditied into a unitary shaped cup 50. A cooling medium such as Wateror air flows into inlet 27 through the opening 29 across the molds 20within the cooling portion 15 into the jacket and out through outlet 26.

The cups are readily removed from the molds 2% which subsequently can berecycled through the apparatus in a similar manner to provide additionalcups. Thus, continuous operation is possible by inserting suitablyfilled molds into the heating section; continually forcing a column ofmolds through the apparatus foaming the expandable plastic material andsubsequently cooling it to prepare the desired objects. Although themolds illustrated have the form of a cup, a wide variety of otherconfigurations may be utilized, such as soap dishes, baskets, boxes andthe like. Such shapes are readily formed employing mating molds. Moreintricate shapes are readily fabricated by employing inserts havingappropriate dimensions.

Molds for the practice of the present invention are advantageouslyprepared in accordance with the teaching of United States Patent2,181,874, wherein induction heater construction and the principles ofheating and distributing the heat in a bimetallic body are set forth.Other heating means are readily employed in the practice of theinvention such as steam, resistance heating, and the like.

The heating means chosen for a particular embodiment will primarily bedependent on the power sources available and the particularconfiguration of the object desired. For example, in the continuousmanufacture of foam plastic toroids, advantageously, steam, hot gas orliquid circulated throughout a plurality of symmetrical perforated moldsis employed. Generally, when employing a liquid as a heating medium forthe molds and circulating it through the passageway 13, it is generallybeneficial to use the heating section on the bottom and move the moldsin an upward direction. Alternately, when steam is employed, often it isadvantageous to position the conduit 12 in a horizontal direction andprovide openings intermediate between heating section 14 and the coolingsection 15 to provide for the escape of condensate.

Typical expandable particulate material which may be employed in thepractice of the invention is described in United States Patents2,744,291 and 2,787,809. Commercially, the most popular of the materialsdescribed in these patents are polystyrene beads having a volatileliquid entrapped within, such as pentane or low boilingfluorohalocarbons.

When thin objects such as cups are prepared, it is advantageous toprovide a means of distributing a particulate foamable materialuniformly over one and sometimes two surfaces of the mold. This isreadily achieved by applying an adhesive to the surface or surfaces ofthe mold where it is desired to position the expandable material.Suitable adhesives often comprise aqueous starch solutions, solutions ofgum agar, sugar solutions, and frequently sufficient adhesion anddistribution may be attained by wetting the surfaces of the mold with anaqueous solution of detergent or glycerine. When water soluble adhesivesare employed, they are readily rinsed from the surface of the formedplastic object.

By way of further illustration, a plurality of molds were constructedsubstantially as shown in FIGURE 2 employing low carbon steel andaluminum having a diameter of about 3 inches and designed to form a cupabout 3% inches long and about 2 inches in diameter at the base. Anapparatus comprised a 20 inch long passageway; a 10 inch portion of oneend was wound with 58 turns of /4 inch (nominal) copper tubing havingattached thereto a water supply. The coil of copper tubing was connectedto a power source which delivered to the coil about 300 amperes at 6volts, 60 cycles alternating current. The remaining 10 inches of theapparatus was jacketed with a water jacket and provided with means tointroduce water into the passageway to assist in cooling the molds. Themolds were so constructed and arranged to produce a cup which wasidentical in size with a cup produced by conventional moldingtechniques. The female portion of the mold was sprayed with about A of agram of an aqueous solution consisting of about 50 percent commercial(Karo) corn syrup and about /2 percent of a nonionic detergentcommercially available under the trade name Joy. This solution wasuniformly spread over the mold surface. The cavity was subsequentlyfilled with partly foamed polystyrene beads passing through a 22 meshscreen and retained on a 40 mesh screen. Excess beads were poured out ofthe cavity and a uniform layer of beads remained coating the femalesurface. A cup liner was vacuum formed from a 2 mil thick polystyrenesheet and was placed over the male portion of the mating mold. The lineron the male portion was placed against the surface presented by thepartly expanded beads adhered to the female portion of the mold and theassembled molds placed in one end of the heating passageway. Similarsets of molds were coated with partly expanded polystyrene beads andliners and inserted into the heating passageway forcing the moldsalready in the passageway toward the cooling section. When thepassageway was completely filled with molds, those issuing from theopposite end of the passageway were removed and opened. Well formed cupswere obtained weighing about 2 grams. The foamed polystyrene wasintegrally bonded to the polystyrene liner. By way of contrast, cupsformed by the melding of expandable particulate polystyrene by themethods of the prior art weighed 5 grams. Cups formed in accordance withthe prior art when tested occasionally showed a tendency toward leakage.No tendency to leak was observed in the cups in accordance with theinvention. In a similar manner, other expandable particulate polymericcompositions are readily shaped into a wire variety of articlesincluding cups, discs, trays, boxes, stoppers, bungs and ornamentalconfigurations.

As is apparent from the foregoing specification, the apparatus andmethod of the present invention are sus ceptible of being embodied withvarious alterations and modifications which may differ particularly fromthose that have been described in the preceding specification anddescription. For this reason, it is to be fully understood that all ofthe foregoing is intended to be merely iliustrative and is not to beconstrued or interpreted as being restrictive or otherwise limiting ofthe present invention, excepting as it is set forth and defined in thehereto appended claims.

What is claimed is:

1. Method of forming a plurality of foamed unitary thermoplasticresinous objects comprising providing a first mold having a desiredconfiguration placing within said desired configuration a quantity ofresinous thermoplastic expandable material, placing adjacent said firstmold a second mold, having a desired configuration and confining saidexpandable thermoplastic material by means of said first and secondmolds, adding expandable thermoplastic material to the configuration ofsaid second mold confining the material therein with a third mold havinga desired configuration continually sequentially heating said molds andcontents thereof to a temperature sufficient to expand the particulatethermoplastic material, sequentially cooling said molds and removing thefoamed thermoplastic object therefrom.

2. Method of forming a plurality of foamed unitary polystyrene objectscomprising: providing a first mold having a desired configuration,placing within said desired configuration a quantity of particulateexpandable polystyrene, placing adjacent said first mold a second mold,having a desired configuration and confining said particulate expandablepolystyrene by means of said first and second molds, adding particulateexpandable polystyrene to the configuration of said second moldconfining the material therein with a third mold having a desiredconfiguration, continually sequentially heating molds and contentsthereof to a temperaure snfficient to expand the particulatethermoplastic material, sequentially cooling said molds and removingfoamed thermoplastic objects therefrom.

3. Method of continually forming a plurality of foamed polystyrene cupsemploying a plurality of like molds providing a first mold having agenerally hollow frusto-tconical configuration, placing within saidhollow configuration a quantity of particulate expandable polystyrene,placing adjacent said first mold a second mold, having a configurationsimilar to said first mold and confining said expandable thermoplasticmaterial by means of said first and second molds, adding particulateexpandable polystyrene to the hollow configuration of said second moldconfining the expandable polystyrene therein with a third mold having aconfiguration similar to said first mold, continually sequentiallyheating said molds and contents thereof to a temperature sufficient toexpand the particulate polystyrene, sequentially cooling said molds andremoving a foamed polystyrene cup therefrom.

4. The method of claim 3, including the step of applying an adhesive tothe wall of the mold to retain said particulate material in a generallycup-like configuration.

5. The method of claim 3, wherein an unexpanded non-porous plastic cupliner is positioned between said expandable polystyrene and the adjacentmold.

6. The method of claim 1, including the step of applying an adhesive tothe wall of the mold to retain said particulate material in a generallycup-like configuration.

7. The method of claim 1, wherein an unexpanded nonporous plastic cupliner is positioned between said expandable polystyrene and the adjacentmold.

References Cited by the Examiner UNITED STATES PATENTS 1,566,500 12/1925 Northrup.

1,689,584 10/1928 Grupe 264-91 2,560,491 7/1951 Smith et al 264-120 XR2,787,809 4/1957 St-astny 264-53 2,803,046 8/1957 Brennan 22-75 XR2,959,829 11/ 1960 Brennan 22-75 XR 2,976,577 3/1961 Gould 264-2,977,639 4/ 1961 Barkhuff et al. 264-45 3,000,058 9/1961 Thielen 264-453,068,526 12/1962 Croan 264-51 3,079,630 3/1963 Orr 264-51 3,080,2673/1963 Schmalz 264-45 XR ALEXANDER H. BRODMERKEL, Primary Examiner.

ROBERT F. WHITE, Examiner.

P. E. ANDERSON, Assistant Examiner.

1. METHOD OF FORMING A PLURALITY OF FOAMED UNITARY THERMOPLASTICRESINOUS OBJECTS COMPRISING PROVIDING A FIRST MOLD HAVING A DESIREDCONFIGRUATION PLACING WITHIN SAID DESIRED CONFIGURATION QUANTITY OFRESINOUS THERMOPLASTIC EXPANDABLE MATERIAL, PLACING ADJACENT SAID FIRSTMOLD A SECOND MOLD, HAVING A DESIRED CONFIGURATION AND CONFINING SAIDEXPANDABLE THERMOPLASTIC MATERIAL BY MEANS OF SAID FIRST AND SECONDMOLDS, ADDING EXPANDABLE THERMOPLASTIC MATERIAL TO THE CONFIGURATION OFSAID SECOND MOLD CONFINING THE MATERIAL THEREIN WITH A THIRD MOLD HAVINGA DESIRED CONFIGURATION CONTINUALLY SEQUENTIALLY HEATING SAID MOLDS ANDCONTENTS THEEOF TO A TEMPERATURE SUFFICIENT TO EXPAND THE PARTICULATETHERMOPLASTIC MATERIAL, SEQUENTIALLY COOLING SAID MOLDS AND REMOVING THEFOAMED THERMOPLASTIC OBJECT THEREFROM.
 7. THE METHOD OF CLAIM 1, WHEREINAN UNEXPANDED NON-POROUS PLASTIC CUP LINER IS POSITIONED BETWEEN SAIDEXPANDABLE POLYSTYRENE AND THE ADJACENT MOLD.